Nature nurtures

Thursday

May 31, 2007 at 12:01 AMMay 31, 2007 at 4:44 AM

Chris Bergeron/Daily News staff

Some devoted dads would sit like emperor penguins atop their kids for a few months until they were ready to move out. But a few, like brown-headed cowbirds, would just leave their babies with strangers expecting them to feed and raise them.

The complex ways birds nurture and protect their young is explored in "Nests & Eggs," an informative and fascinating exhibit at the Harvard Museum of Natural History in Cambridge.

This is one of those shows about something that seems as ordinary as blue jays screeching in your backyard or pooping on your windshield. But "Nests & Eggs" leaves you marveling at nature's fabulous diversity.

Drawn from the museum's vast collection, it features more than 100 winged wonders from around the world who each seem to build nests, lay eggs and feed their young in their own style.

"I think visitors will come away with a newfound appreciation for the beauty and variety of the natural world," said Janis C. Sacco, HMNH director of exhibitions.

It does not matter whether you are a seasoned birder or cannot tell Daffy Duck from a bald eagle. These stuffed birds, their fragile eggs and elaborate nests are natural works of art.

Yet, they are also the physical representations of a seemingly miraculous natural genius - some would say it's only evolution at work - that drives their adaptive responses.

Sacco observed that nests and eggs "yield lots of information" about how various kinds of birds live in their habitats and interact with others.

"Nests & Eggs" will be displayed in the Changing Exhibits Gallery through 2008. It was organized by the HMNH's Exhibits Department.

Visitors will see a fossilized dinosaur egg and the basketball-sized egg of an extinct elephant bird that is as large as 180 hen eggs. Kingfishers lay round eggs while hummingbirds lay long cylindrical eggs the size of a coffee bean.

The show includes two videos capturing varied birds building nests in remarkable close-ups.

At its considerable best, "Nests & Eggs" should kindle for children and adults a sense of wonder at the everyday miracles splashing in your birdbath and the customized nests they build.

"This exhibit will inspire visitors to look more closely at the world around them, to see and think about the familiar in new ways," said Elisabeth Werby, the museum's executive director.

Anyone who thought birds built generic nests is - oh, well - a bird brain.

Why do ospreys build tangled nests atop telephone poles while chimney swifts use their own saliva to cement dead twigs together? And where did they both live before humans invented telephones and chimneys?

And how come ostriches just scrape away surface vegetation for their chicks while ruby-throated hummingbirds line their nests with soft dandelions, cattail or thistle down and camouflage them with lichen?

"Almost every bird has developed its own response to meet the particular challenges it faces in their own habitat," explained Sacco.

While reluctant to generalize, Sacco said the exhibit divides hatchlings into two divergent categories, precocial and altricial.

For example, kiwi chicks are considered precocial because they are capable of hunting food and caring for themselves shortly after hatching. On the other hand, the much smaller chicks of northern harriers are described as altricial because they must be carefully tended for 30 to 40 days after hatching.

As a general rule, birds with altricial hatchlings build more sophisticated nests to protect their vulnerable young.

While killdeer chicks are precocial, their parents protect them from predators with a remarkable bit of subterfuge known as the "broken wing display," said Sacco.

If a predator approaches its hatchlings, an adult killdeer lures it away by pretending to have a damaged wing. After drawing the threat away from its chicks, it finally "recovers" and flies away issuing a loud "kill dee" squawk.

Sacco said the exhibit addresses several fundamental questions about the nature of eggs, nests and behavioral patterns associated with nurturing the young.

Visitors may be surprised, she said, to learn a bird's nest "is more like a nursery than a home" because birds of all species build them primarily to incubate their eggs and raise their chicks.

While nests differ enormously, Sacco stressed each variation provides important clues into a species' reproductive habits, behavior and evolutionary history.

Unlike their human counterparts, size doesn't much matter when it comes to nest builders. In fact, bigger birds like herons and hawks are careless builders who reuse their nests year after year while smaller birds construct more sophisticated nests by scavenging several different kinds of material.

Throughout the exhibit, one clear lesson emerges: nature is economical.

Eggs are white or pale blue when there is no benefit to camouflage because there is a protective parent or a secure nest. But birds lay speckled, streaked or mottled eggs when their young are typically exposed to predators.

Some birds prefer to go without nests but even this varies.

Murres just lay their eggs on barren ledges. White terns lay their eggs precariously on the fork of a tree branch while a male emperor penguin holds its mate's egg on his feet for 65 days, incubating it under a roll of belly skin.

For Sacco, brown-headed cowbirds display a rare nesting strategy called "brood parasitism" in which the mother lays her eggs in other birds' nests.

In many cases, the "host" mother is programmed to feed any squawking chick in its nest and often the bigger, earlier-hatching cowbirds get a larger share of food than its nest mates.

For birds and humans, life is not always fair.

THE ESSENTIALS:

The Harvard Museum of Natural History is located on 26 Oxford St., Cambridge.
All the HMNH exhibits are open daily from 9 a.m. to 5 p.m. The museum is closed New Year's Day, Thanksgiving, Christmas Eve and Day.
Tickets: Adults, $9; seniors and non-Harvard students, $7; children, 3-18, $6. It is free to the public Sunday mornings from 9 a.m. to noon and Wednesday afternoon from 3 to 5 p.m., September through May.
The museum is wheelchair accessible. For more information, call 617-495-3045 or visit the Internet Web site, www.hmnh.harvard.edu.
On Saturday, June 2, at 8 a.m., there will be an EGGStravaganza Family Breakfast. Non-member guests: $10 for children 12 and under; $15 for adults.

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